Austenitic stainless steel



United States Patent Otfice 3,201,236 AUSTENITIC STAINLESS STEEL JosephR. Mitchell, Chicago, and Mary E. Potter, Thornton Township, CookCounty, Ill., assignors to United States Steel Corporation, acorporation of New Jersey No Drawing. Filed Mar. 16, 1964, Ser. No.352,314 5 Claims. (Cl- 75-124) This application is acontinuation-in-part of application Serial No. 117,263, filed June 15,1961, now abandoned, which was a continuation-in-part of applicationSerial No. 822,211, filed June 23, 1959, also abandoned.

This invention relates to an aluminum-bearing, nonage-hardeningaustenitic fuel.

Steels possessing a high strength,; along with goodfcorrosion resistanceand high oxidation resistance are desirable for many missile andaeroplane applications. For such uses, it is essential that the steel bereadily hot and cold formable and have good tensile and impact ductileproperties. Aluminum is known to provide good scaling properties at hightemperatures but. prior art steels containing suificient aluminum toprovide enhanced resistance to corrosion or scaling at high temperaturesare ferritic and have had such poor cold forging and ductile propertiesthat they were not suitable for the foregoing applications.

It is accordingly an object of the present invention to provide anaustenitic steel containing high aluminum contents which combines goodcorrosion resistance and oxidation resistance at high temperature alongwith high strength, good tensile and impact ductility and good hot andcold forming properties;

It is another object to provide such properties without the use ofexpensive alloying ingredients.

We have discovered that the foregoing properties can be obtained in ahigh aluminum steel if the aluminum content is balanced with respect tochromium and which contains carbon and manganese in proportioned amountsto render the steel austenitic. In its broader aspects the steel willcontain the following as essential ingredients.

wherein the carbon, manganese, chromium and aluminum Patented Aug. 17,1965 in the chromium and aluminum are balanced within the followinglimits:

Percent 1 chromium=percent aluminum- 1.5

to Percent ehromium=percent aluminum-{4.5

with the total of percent chromium plus percent aluminum being less than17 and with the remainder iron and other elements in amounts which donot adversely affect the properties.

Desirable results can be obtained with the total percent chromium pluspercent aluminum less than 17. However, for the best balance of strengthtensile and impact ductility and atmospheric corrosion and oxidationresistance, we prefer the total percent chromium plus percent aluminumto fall within the range of about 9 to 16. Thus a preferred range is asfollows:

Percent Carbon .40 to .90 Manganese 14.0 to 18.0 Silicon .35 to .75Chromium 4.5 to 8.50 Aluminum 3.75 to 8.50

with the total of'percent chromium plus percent aluminum being between 9and 16 and with the remainder iron and other elements in amounts whichdo not adversely affect the properties.

Some preferred typical examples of steels are as follows:

Car

Sllimn ry-i=5? Percent Chromium percent Aluminum-..

with the balance substantially iron.

The composition of a number of heats of steel illustra tive of ourinvention are given :in the following Table I: t

TABLE LACHEMICAL coMPosmoN GROUP I a Chemical Composition, WeightPercent Heat Number Total C M11 P B 81 Cr A1 1110 N1 percent CPI-AlTABLE IContinued GROUP 10 GROUP 11 GROUP 110 Group I steels in Table Ihave a range of percent high to maintain an austenitic structure withthe use of chromium plus percent aluminum less than 17 with 14 loweredcarbon contents. Group 1a steels are modified to 18% manganese andshowing carbon levels required with molybdenum or nickel and Group Haare stee to develop an austenitic structure. The Group II steels 30modified with molybdenum. largely have percent plus percent aluminumlevels in The tensile and impact properties of the steels of Table therange of 11 to 15% with the manganese sufiiciently I are given in thefollowing Table II:

TABLE II.-'IENSILE AND IMPACT PROPERTIES IN THE ANNEALED CONDITION GROUPI Total Yield Tensile Elongation Reduction V-Notch Cherpy Heat NumberCr+Al. Strength Strength, in 2", 01 Area, Impact Energy at Percent (0.2%O flset), p.s.i. Percent Percent Minus 60 F. FtJLb.

GBO UP 10 1L890 14. 11 Not Tested Not Tested Not Tested Not Tested b11L881 14. 29 Not Tested N at Tested Not Tested Not Tested 72 GROUP '11GROUP 110 G R UP 1 Total Weight Gain, Appearance Alter Heat NumberCr-i-Al, mgJsq. cm. Exposure Percent 3. 36 72. 2 Heavy layers of loosescale. 6. 46 33. 5 Do. it. 17 1. 1 Fine dust-like scale.

s. 54. 8.1 Do. 9. 12 1. 2 Do. 22. 29 1. 5 Do. 15. 41 Not tested Bright,no evidence of scale. 15.69 0.2

GROUP Ia H4890 M. i1 058 Discolored. iLBt-ll 1%. 29 6. 1 Fine dnst-likescale.

G R0 U P H 11. 74 l. 6 Trace of loose'scale. 12. 56 Not tested Do. 12.83 0. 9 Do. 13. ll 0. 8 Do. 13. 37 0. 6 D0. l3. 75 0.7 D0. 13. 7! 2. 9Fine loose scale. 13. 98 3. 8 D0. 14. 71 4. 7 D0. 15. 28 1. 9 D0.

6. 98 6. 9 Fine loose scale. 9. 88 13. 8 D0. 12. 93 2. 2 D0.

i3 lV.--- ilESULTS OF 180 DEGREE BEN d Typical properties of Steels A, Band C in. the annealed condition are given in the following 'liablc V:

TABLE V PROPE RI1ES-ANNEALED Steel 1%. is characterized by a completelyaustcntic strnc-- ture in the solution annealed condition. A unique ice.ture of this composition is that it remains relatively of carbideprecipitation after forging and after anncalin and sensitizing in therange of iiiiii to 1408: P. it is further characterized by high tensileand yield strengths. high tensile ductility, excellent impact ductility,and fair oxidation resistance. This steel can "be hot and cold formedand provides the foregoing combinations of pro perties economically. Atypical use is for automobile muffiers and for other applicationsrequiring these im proved properties at minimum cost.

Steel B is characterized by a completely austeniiic structure in theannealed condition. It is further characterized by high tensile andyield strengths, high tensile ductility, high impact ductility, goodoxidation resistance at elevated temperatures, and atmospheric corrosionrcsist-= ance. This steel can be hot and cold formed and provides theproperties of Steel A along with improved atmos pheric corrosionresistance and improved elevated-tom perature oxidation resistance.

. AB" D 'l ii? iii 'iilili ANNEALED AND SENSITIZED CONDITION GROUP IHeat Total As Annealed (/6 Hr. at 2,000" Annealed and sensitized NumberCr-l-Al. F., W.Q.) (2,000 F., W.Q.+2 Hrs.

Percent at 1,250" F., AC.)

3. 36 No evidence of cracking No evidence of cracking. 6.46 do Do. 8. 17Do. 2.5 1. Do. 9. 42 Do. 12:29 Do. 15.41 D0. 15.69 Brittle break at.start of bending.

GROUP in H.830 i4. 11 N 0 evidence of cracking No evidence of cracking.iLfiSl 14.29 .do Do.

GROUP II 11. 74 No evidence of cracking. No evidence oi cracking. 12.56d0--.. D0. 12.83 .410- Do. 13. 11 .do. Do. 13.37 .do. Do. 13. 75 .--doDo. 13. 77 do Do. 13. 58 ...do. Do. 14.71 ...do. Do. 15. 28 ..--do Do.

GROUP He.

6. 98 No evidence oi cracking"-.- -No evidence oi cracking. 9. 88 do Do.12. 93 do D0.

' such uses as automobile trim since it has good corrosion resistanceand good cold workability.

Contradistinguished from the foregoing is the following steel which is atypical steel of the prior art.

Chemical Composition. Weight Percent ance, good cold forma-bility andlow temperature impact properties, said steel consisting essentially of1 HeatNo. Pi -03:1 C be 25 Perceing H ar 11 to 0 Mn 81 or A1 m 15Manganese 14.0 to 35.0 Silicon .25 to 1.0 11 1125 0.99 10.90 0.61 22.112.68 25, Chromium 4.5 to 8.75 Aluminum 3.5 to 8.75 Balance iron.

The annealed and impact properties of this Steel 1L1 125 are given inthe following Table VI:

dation resistance along with good hot and cold formabiiity properties.

While we have shown and describedseveral specific embodiments of ourinvention, it will be'understood that these embodiments are merely forthe purpose of illustration and description and that various other formsmay be devised within the scope of our invention, as defined "in theappended claims.

We claim:

1. An aluminum-bearing, non-age-hardening aus-tenitic steelcharacterized by high temperature oxidation resistwherein the carbon,manganese, chromium and aluminum are balanced to provide an austeniticstructure and where- TABLE VI.-ANNEALED TENSILE AND IMPACT Annealed at2,000 F. and waterjquenched Oxidation and cold formability tests on thissteel are given in the following Tables VII and VIII:

TABLE VII.RESULTS OF 78-HOUR OXIDATION TEST AT 1500 P. IN THE ANNEALEDCONDI- TION Heat No. Total Percent Cr+ Weight Gain, mg]

Percent Al cm.

in the chromium and aluminum are balanced within the following limitsPercent chromium=percent aluminum-1.5

Percent chromium=percent aluminum+1.5

with the total of percent chromium plus percent aluminum being less than'17.

2. An aluminum-bearing, non-age-hardening austenitic steel characterizedby high temperature oxidation resistance, good cold formability and lowtemperature impact properties, said steel consisting essentially ofPercent TABLE VIE-RESULTS OF 180 DEGREE BEND Carbon .40 to .90

TEST Manganese 14.0 to 18.0

Silicon .35 to .75

a] Annealed H Ann 1 d d Chromium 4.5 to 8.50

Nigger 032m, irwoman? tized 0 Aluminum and to percent Hrs. at 1250F.,A.G.)

wherein the carbon, manganese, chromium and aluminum 5 25,39 grime r k tstart Brittle br at are balanced to provide an austenitic structure andwhere Ofbendingvibendingin the chromium and aluminum are balanced withinthe following limits Percent chromium=percent aluminum-1.5 The poortensile and impact ductility of such prior steel of Heat No. 1Ll125 isclearly shown by the foregoing data- Percent chromium=percent aluminum+1.5

From the foregoing it is apparent that the steels of thisinvention arecharacterized :by an austenitic structure in the solution annealedcondition, high tensile and yield strengths, good tensile and impactductility, good atmospheric corrosion resistance andelevated-temperature oxiwith the total of percent chromium plus percentaluminum being between 9 and 16.

3. An aluminum-bearing, non-agehardening auste'nitic steel characterizedby good corrosion resistance, high tern- 9 perature oxidationresistance, low temperature impact properties, high tensile propertiesand good cold formability, said steel consisting essentially of with thebalance iron.

4. An aluminum-bearing, non-age-hardening austenitic steel characterizedby good corrosion resistance, high temperature oxidation resistance, lowtemperature impact properties, high tensile properties and good coldformability, said steel consisting essentially of Percent Carbon About0.80 Manganese About 16.0 Silicon About 0.50

A 10 A Percent Chromium About 7.00 Aluminum About 6.00

with the balance iron.

5. An aluminum-bearing, non-age-hardening austenitic steel characterizedby good corrosion resistance, high temperat'ure oxidation resistance,low temperature impact properties, high tensile properties and good coldformability, said steel consisting essentially of Percent Carbon About0.90 Manganese About 17.00 Silicon About 0.50 Chromium About 8.00

Aluminum About 7.00

with the balance iron.

No references cited.

DAVID L. RECK, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,201,230 August 17, 1965 Joseph R. Mitchell et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line 14, for "fuel" read steel column 2, TABLE I, secondcolumn, line 6 thereof, for "0.85" read 0.86 column 3, TABLEI-Continued, GROUP Ia, fourth column, line 1 thereof, for "0.103" read0.013 same table, tenth column, line 2 thereof, for "0.96" read 1.96same table, GROU PRII, fifth column, line 1 thereof, for "0.104" read0.014 same table, eighth column, line 4 thereof, for "5.80" read 5.90same column 3, line 31, after "percent", first occurrence, insertchromium column 5, TABLE III, GROUP I, fourth column, line 7 thereof,strike out "Bright, no evidence of scale.", and insert the same in thesame column, line 8, and opposite Heat Number ',1L724"; same table,GROUP II, fourth column, line 2 thereof, strike out "Do.".

Signed and sealed this 5th day of April 1966.

(SEAL) "Attest:

EDWARD J. BRENNER Commissioner of Patents ERNEST W. SWIDER AttestingOfficer

1. AN ALUMINUM-BEARING, NON-AGE-HARDENING AUSTENITIC STEEL CHARACTERIZEDBY HIGH TEMPERATURE OXIDATION RESISTANCE, GOOD COLD FORMABILITY AND LOWTEMPERATURE IMPACT PROPERTIES, SAID STEEL CONSISTING ESSENTIALLY OF